The LEAPSECS mailing list has been discussing the issue of implementing leap seconds in UTC for seven years. There is rarely any consensus between those who want to abandon leap seconds and those who want to keep them. There is on occasion something to which there is not strong objection. Last year LEAPSECS fell silent at the suggestion that leap seconds should be announced five years in advance (instead of the current practice of 6 months and requirement of only 8 weeks).
The point is that changing civil time in any fashion is extremely disruptive (see Hugo Chavez and Venezuela last week). If the international technical community would agree that five years of advance warning is required, then the local legislative and bureaucratic folks who modify daylight time might get the message.
It's a dream.
Daniel Kleppner of MIT contributed an article to Physics Today which ruminated on the problems that clocks like this will have for international timekeeping. The trick is that the clocks will be able to see the diurnal variations in general relativistic gravitational potential. No two clocks like this on the surface of the earth will ever be able to agree with each other. A whole new set of computational protocols for combining their results into International Atomic Time (TAI) will be necessary.
Have a look at an old ephemeris and see the large numbers of tabulations of quantities with respect to date. For the sake of ease of typesetting it was commonplace to have tables with dates such as January 0, 5, 10, 15, 20, 25, 30, and 35. That avoided the need to redundantly set more lead into the matrix for the name of the month o nevery single line of the tables. In the case of tables being interpreted by humans there was no expectation of raising some sort of input exception because in the full context the meaning was pretty obvious.
To within about one part in 1.E12 the ephemeris second is identical to the SI second defined by the cesium resonance. In 1977 the length of the second of TAI was changed so as to conform better with the preferred definition of the SI second. Before 1977 TAI and UTC ticked faster than they do now. Astronomers did not object to the change in rate of TAI because it was within the uncertainty of the original definition of the ephemeris second.
The illusion extends to constellations as well. Take a look at a constellation when it is up high and it seems smaller than when it is near the horizon.
The joint IAU/IAG/COSPAR committee who wrote this triennial report decides. Some objects have surface features that define the origin. Other objects simply have conventional longitudes defined presuming that they are tidally locked to their parent body. Until further notice Titan is one of the latter.
To be sure, this is merely that there was no leap second yesterday. Slashdot has previously seen another story about the possibility that leap seconds might be discontinued permanently. Within the confines of that are links to everything that you could ever want to know about leap seconds, earth rotation, history of internecine wars between astronomers and physicists about time, etc.
It means that the POSIX era counted by 32-bit time_t will end sooner as
counted by elapsed SI seconds, but there will be no
change in the date read by the clock so long as UTC retains its current definition.
In the same class is the ITU who have a similar
model of charging. Among their standards is
ITU-R TF.460 which defines coordinated Universal time (UTC). If you've ever wondered why leap seconds are so poorly implemented by your computer, this proprietary standard is part of the reason. It is evident that the original authors of the POSIX standard had not read it before they declared that a Unix time_t should indicate time in UTC.
At NOAO the Unix lpd has long been used as the mechanism for Save the Bits, which is the means by which they and several other observatories archive all of the data acquired at their telescopes.
The fact that the earth's rotation is slowing down
has been known for most of a century. That its speed varies seasonally has been known since the 1930s. That the speed varies daily under the influence of the winds and tides has been known since the 1980s. That its speed varies daily due to the oblateness of the solid inner core has been known since the 1990s. That its speed varies on a timetable of decades under the influence of core/mantle currents is still being measured.
All of these measurements are made under the purview of the International Earth Rotation Service. There are models for all manner of astrophysical and geophysical effects considered in the Conventions
that are used when reducing the data.
The way that solar noon is kept at civil time noon is by inserting leap seconds. In most places civil time is offset directly from UTC. When a leap second is inserted the day is 86401 seconds long.
This irregularity upsets some kinds of timekeeping systems, and as a result there has been discussion that leap seconds should be abolished. That would cause noon to drift away from noon. That may not be a good thing.
Why would I pay to go to Hawaii when I can eavesdrop on every image from my living room? Or I could head over to the office and use the video link to converse and smile with him from California. I'm one of the engineering team who built the instrument (HIRES) that Marcy will be using.
My lawyer neighbor says this is because they don't want computer people because we think logically and are not emotional. Have other slashdot readers had similar experiences with the judicial system?
Does your lawyer neighbor actually try jury cases and use lack of emotion to strike jurors? If so I could probably guess several elements of his temperament, and that leaves him in a position to be manipulated.
Neither my degree nor my programming profession has kept me off juries. Don't get a complex, the sixth time may put you in a room with a dozen folks from outside your social circle and a patriotic mission.
Slashdot Mirror
Problem exists between keyboard and chair, and the article does not address that aspect nor give any good workaround.
I suppose I'll have to make do with Jamie Zawinski's version as I retire the real ones.
A book by Joe Haldeman.
The LEAPSECS mailing list has been discussing the issue of implementing leap seconds in UTC for seven years. There is rarely any consensus between those who want to abandon leap seconds and those who want to keep them. There is on occasion something to which there is not strong objection. Last year LEAPSECS fell silent at the suggestion that leap seconds should be announced five years in advance (instead of the current practice of 6 months and requirement of only 8 weeks). The point is that changing civil time in any fashion is extremely disruptive (see Hugo Chavez and Venezuela last week). If the international technical community would agree that five years of advance warning is required, then the local legislative and bureaucratic folks who modify daylight time might get the message. It's a dream.
Read this article about Ted Molczan and the amateur satellite tracking. It's hard to believe the French have any leverage here.
We're rather experienced with the ritual destruction of keyboards. Quality and durability varies wildly from one to another.
I'm not sure where the scientific part is.
The engineers are coming up with new ideas faster than we can assimilate them? I'm not sure I would have wanted to use that word in this context.
Daniel Kleppner of MIT contributed an article to Physics Today which ruminated on the problems that clocks like this will have for international timekeeping. The trick is that the clocks will be able to see the diurnal variations in general relativistic gravitational potential. No two clocks like this on the surface of the earth will ever be able to agree with each other. A whole new set of computational protocols for combining their results into International Atomic Time (TAI) will be necessary.
Have a look at an old ephemeris and see the large numbers of tabulations of quantities with respect to date. For the sake of ease of typesetting it was commonplace to have tables with dates such as January 0, 5, 10, 15, 20, 25, 30, and 35. That avoided the need to redundantly set more lead into the matrix for the name of the month o nevery single line of the tables. In the case of tables being interpreted by humans there was no expectation of raising some sort of input exception because in the full context the meaning was pretty obvious.
To within about one part in 1.E12 the ephemeris second is identical to the SI second defined by the cesium resonance. In 1977 the length of the second of TAI was changed so as to conform better with the preferred definition of the SI second. Before 1977 TAI and UTC ticked faster than they do now. Astronomers did not object to the change in rate of TAI because it was within the uncertainty of the original definition of the ephemeris second.
For a pretty full understanding of what is happening, what has happened, and why, see history of the effort, implications of change, definition of terms
The illusion extends to constellations as well. Take a look at a constellation when it is up high and it seems smaller than when it is near the horizon.
The joint IAU/IAG/COSPAR committee who wrote this triennial report decides. Some objects have surface features that define the origin. Other objects simply have conventional longitudes defined presuming that they are tidally locked to their parent body. Until further notice Titan is one of the latter.
There are three types of lies: lies, damn lies, and statistics.
To be sure, this is merely that there was no leap second yesterday. Slashdot has previously seen another story about the possibility that leap seconds might be discontinued permanently. Within the confines of that are links to everything that you could ever want to know about leap seconds, earth rotation, history of internecine wars between astronomers and physicists about time, etc.
It means that the POSIX era counted by 32-bit time_t will end sooner as counted by elapsed SI seconds, but there will be no change in the date read by the clock so long as UTC retains its current definition.
The World of Astronomy site at Wolfram.com is a bit out of date and does not include the most recent changes in time scales. I recommend this page which describes the history of various time scales.
No, and physicists physicists do admit that they are not perfect. They also have a plan to use pulsars to see just how imperfect the atomic clocks are.
The IERS has a plot showing how the length of day has decreased over the past few years. Curiously, the current phase of accelerated rotation of the crust began right around the time we started adding leap seconds to UTC.
In the same class is the ITU who have a similar model of charging. Among their standards is ITU-R TF.460 which defines coordinated Universal time (UTC). If you've ever wondered why leap seconds are so poorly implemented by your computer, this proprietary standard is part of the reason. It is evident that the original authors of the POSIX standard had not read it before they declared that a Unix time_t should indicate time in UTC.
At NOAO the Unix lpd has long been used as the mechanism for Save the Bits, which is the means by which they and several other observatories archive all of the data acquired at their telescopes.
All of these measurements are made under the purview of the International Earth Rotation Service. There are models for all manner of astrophysical and geophysical effects considered in the Conventions that are used when reducing the data.
The way that solar noon is kept at civil time noon is by inserting leap seconds. In most places civil time is offset directly from UTC. When a leap second is inserted the day is 86401 seconds long.
This irregularity upsets some kinds of timekeeping systems, and as a result there has been discussion that leap seconds should be abolished. That would cause noon to drift away from noon. That may not be a good thing.
Why would I pay to go to Hawaii when I can eavesdrop on every image from my living room? Or I could head over to the office and use the video link to converse and smile with him from California. I'm one of the engineering team who built the instrument (HIRES) that Marcy will be using.
Does your lawyer neighbor actually try jury cases and use lack of emotion to strike jurors? If so I could probably guess several elements of his temperament, and that leaves him in a position to be manipulated.
Neither my degree nor my programming profession has kept me off juries. Don't get a complex, the sixth time may put you in a room with a dozen folks from outside your social circle and a patriotic mission.